Project Summary/Abstract Defining Novel Mechanisms underlying Human Arrhythmogenic Cardiomyopathy Arrhythmogenic cardiomyopathy (AC, also termed ARVC) is a complex and potentially fatal disease commonly associated with ventricular arrhythmias in young adults. AC is an inherited disorder primarily associated with loss-of-function gene variants in cardiac desmosomal proteins. However, as the full spectrum of AC disease genes is still unknown, we unfortunately lack critical information essential for the diagnosis and treatment of this devastating disease. We seek to identify a new genetic/molecular mechanism for human AC. Our data that include clinical, pathological, genetic, in vivo, biochemical, and molecular studies support a new and unexpected molecular mechanism underlying human AC. Specifically, we have identified ANK2 (encodes AnkB) as a human AC candidate gene. Notably, unlike most AC disease genes, AnkB is not a desmosomal protein. Patients harboring ANK2 loss-of-function variants display AC resulting in sudden cardiac death. A new mouse model of cardiac-restricted AnkB deletion phenocopies human AC displaying structural remodeling, fibrosis, and early mortality. Finally, our data support an unanticipated mechanism for cardiac AnkB. Specifically, our data support that: 1) AnkB directly binds ?-catenin, a molecule tightly linked with cardiac Wnt signaling in AC, and 2) ?-catenin regulation is altered in hearts of human ANK2 AC and AnkB cKO hearts. Our objective is to define the molecular mechanisms underlying AnkB dysfunction in human AC. Our preliminary data support a conclusion that AnkB is critical for cardiac structural and electrical function, and plays an unexpected role in ?-catenin regulation. Further, our data supports that AnkB dysfunction in humans and mice results in maladaptive remodeling, heart failure, arrhythmia, and ultimately early death associated with altered ?-catenin activity.